The present invention relates to materials and methods relating to cell control and cell suppression.
One of the greatest challenges is to devise strategies for the selective control of the activities of particular cells. For example, a strategy for the inactivation of harmful cell responses such as undesirable immune responses, as in the case of IgE-mediated allergies, auto-immune disease, rejection of transplants.
UK Patent No. 1578348 and U.S. Pat. No. 4261973 disclose that an antigen or allergen such as ovalbumin (OA), and the non-dialysable constituents of the aqueous extract of ragweed pollen and dog albumin, may be converted to a tolerogen by coupling it to an optimal number (n) of monomethoxypolyethylene glycol (mPEG) molecules. Injection of tolerogenic mPEG conjugates of these antigens/allergens into rats and mice, led to abrogation of the capacity of the mice to mount humoral antibody responses to those immunogenic molecules. Further, these patents describe the establishment in mice of an IgE antibody response by the injection of an allergen comprising dinitrophenylated ovalbumin (DNP-OA). The mice were then treated with an OA-PEG conjugate. It was shown that the administration of the OA-PEG conjugate into the sensitized mice resulted in a very marked decrease of the ability of the mice to mount an immune IgE antibody response not only to OA but also to DNP on subsequent challenge with DNP-OA.
Allergies are caused by a wide variety of substances eg pollens, foods, dust, chemicals collectively referred to hereafter as environmental allergens. Generally speaking allergens are antigens and the terms allergen and antigen may be used interchangeably in the context of this application, but the term allergen is particularly used to denote a type of antigen which induces the production of antibodies of isotype IgE (which mediate Type I allergies) in addition to antibodies of other isotypes as generated in response to common antigens.
UK Patent No. 2238959 followed on from the above work and disclosed that pre-treatment of a recipient with a tolerogen suppresses the immune response not only to the antigen incorporated in the tolerogen, but also to a conjugate of that antigen and at least one additional antigenic moiety which may be a hapten or another unrelated protein. For example, the patent discloses that injection of a tolerogenic mPEG conjugate of human IgG (ie, HIgG(mPEG)25) into mice, prior to administration of conjugates of human IgG with either dinitrophenyl DNP or DNP-keyhole limpet haemocyanin (KLH) (ie, DNP7-HIgG or DNP23-KLH-HIgG), led to the abrogation of the capacity of the mice to mount humoral antibody responses to both human IgG and the conjugated moiety DNP or DNP23-KLH. If, however, the mice pretolerised to HIgG by injection of HIgG(mPEG)25 were injected with a non-covalent mixture of DNP23-KLH and human IgG, the mice mounted normal humoral antibody responses to DNP and KLH, but remained suppressed to human IgG.
The above discussed art concerns the use of mPEG-allergen conjugates to suppress the initial development of an immune response to an antigen (eg human IgG) or allergen (eg OA). However, there is a real need for products and treatment methods which are directed to the control of an already established immune response and hence the alleviation of the associated clinical symptoms.
Certain cellular functions are controlled by the cell membrane with changes in cell activity being mediated by changes in the cell membrane. This will now be discussed in more detail and by way of example only, the discussion is in relation to granulocytes which are involved in the body""s immune response to an allergen.
When an individual is exposed to an allergen which is recognised by that individual""s immune system as being foreign, there will be proliferation of antibody-producing B cells including Bxcex5 cells, ultimately resulting in the formation of IgE antibodies with specificities for the different epitopes presented by the allergen circulating in the blood stream. The Fc region of an IgE antibody (referred to as Fcxcex5) binds with high affinity to Fcxcex5 receptors specific for IgE located in the surface membrane of various types of granulocytes, e.g., mast cells in tissues and basophils in the blood. Typically a mast cell will have 300-600xc3x97103 receptors for the Fc tails of IgE antibodies. The occupation of these receptors by IgE antibodies via their Fc tails results in the production of a cell which is said to be sensitised. Thus the sensitised granulocytes, e.g., mast cells, are effectively coated by IgE antibodies bound to the cell by the interaction of their Fc tails with the cell surface Fcxcex5 receptors. The antigen-binding sites (the Fab arms) of the coating IgE antibodies project into the surrounding medium. Since the Fc tail does not substantially vary from one IgE antibody to another (it is said to be xe2x80x9ccommonxe2x80x9d), a granulocyte may be coated with IgE antibodies of differing specificities.
When the sensitised mast cells or basophils come into contact with a multivalent allergen (ie an allergen having multiple epitopes available for binding to IgE antibodies), the allergen is bound by the Fab regions of different IgE antibodies, each antibody recognizing (ie reacting) the appropriate epitope. This has the effect of cross-linking the Fc receptors of the sensitised cells by the allergen. This results in the destabilisation of the mast cell membranes, followed by degranulation of these cells with the release of vasoactive compounds, such as histamine and heparin from their granules.
The present applicants describe herein experiments which show that if an animal already producing IgE antibodies to an allergen is treated with a conjugate of mPEG and the allergen, granulocytes involved in IgE-mediated inflammation (ie granulocytes coated with IgE antibodies some of which having specificity for the allergen) are inactivated. Thus, a water-soluble covalent conjugate of an allergen with one or more non-immunogenic polymeric molecules (i.e., polymeric chains) can be used to alleviate the symptoms of an already established immune response against the allergen.